Responses of soil aggregation and aggregate-associated carbon and nitrogen in black soil to different long-term fertilization regimes

Long-term cultivation has generated an enormous carbon (C) and nitrogen (N) deficit in black soil. Fertilizer management has been proven to be important to improve aggregate stability and enhance soil C and N stocks, which primarily occur within aggregates. Using a continuous wheat-soybean-maize rotation system in black soil with a 39-year different fertilizer regimes that created a large range in C input (2.03–3.88 Mg C ha−1 yr−1), we investigated long-term fertilization affected soil aggregation and aggregate-associated C and N levels in soil depths of 0–10, 10–20, and 20–40-cm, and assessed aggregate-associated soil organic carbon (SOC) saturation behavior. Across soil depth intervals, application of synthetic fertilizer with or without manure increased macroaggregate turnover, which increased release of silt and clay (SC) within macroaggregates and promoted formation of free microaggregates (free-m) and free-SC. Fertilization increased organic material (straw and manure) input and greatly favored C and N sequestration in macroaggregates (mainly within the SC fraction, because of the high mass proportion) and free-m. Significant linear relationships were observed between the C content in the soil aggregate fraction and C input, indicated that the added C was primarily stored in stable aggregates, suggesting that bulk soil remained SOC-deficient under current fertilizer regimes. Overall, application of large amounts of organic material is an adequate soil management strategy to improve the structure of black soil and increase soil organic carbon and nitrogen sequestration. This strategy will be useful for agricultural sustainable development and mitigation of climate variability.